<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        .main{
            width: 800px;
            height: 400px;
            background-color: #ff0e09;
            position: relative;
            margin: 50px auto;
        }
        .nav{
            width: 400px;
            height: 200px;
            background-color: blueviolet;
            position: absolute;
            left: 200px;
            top:100px;
        }
    </style>
</head>
<body>
   <div class="main">
       <div class="nav"></div>
   </div>
</body>
</html>